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ENGLISH 三上悠亚最经典贴吧"At dawn the bombardment started again, but only the front was seriously damaged. The garrison stood as firm as a rock. Here and there the beginnings of a fire were soon extinguished.A FEW words by way of introduction.The loss of effect by the inertia of the pieces acted upon increases with the weight of the work; not only the loss of power, but also the expense of heating increases with the size of the pieces. There is, however, such a difference in the mechanical conditions between light and heavy forging that for any but a heavy class of work there would be more lost than gained in attempting to operate on both sides of pieces at the same time.
When a tool is guided by turning on points, the movement is perfect, and the straightness or parallelism of holes bored in this manner is dependent only on the truth of the carriage movement. This plan of boring is employed for small steam cylinders, cylindrical valve seats, and in cases where accuracy is essential.
(1.) Why are shaping machines better adapted than planing machines for planing slots, key-ways, and so on?(2.) What objects are gained by a quick return motion of the cutter bar of shaping machines?"No!"
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Some makers of steam-hammers have so perfected the automatic class, that they may be instantly changed so as to work with either dead blows or elastic blows at pleasure, thereby combining all the advantages of both principles. This brings the steam-hammer where it is hard to imagine a want of farther improvement.
In cutting screws it is best not to refer to that mistaken convenience called a wheel list, usually stamped on some part of engine lathes to aid in selecting wheels. A screw to  be cut is to the lead screw on a lathe as the wheel on the screw is to the wheel on the spindle, and every workman should be familiar with so simple a matter as computing wheels for screw cutting, when there is but one train of wheels. Wheels for screw cutting may be computed not only quite as soon as read from an index, but the advantage of being familiar with wheel changes is very important in other cases, and frequently such combinations have to be made when there is not an index at hand.The successful application of the pneumatic system at the Mont Cenis Tunnel in Italy, and at the Hoosac Tunnel in America, has demonstrated the value of the system where the air not only served to transmit power to operate the machinery but to ventilate the mines at the same time. Air brakes for railway trains are another example illustrating the advantages of pneumatic transmission; the force being multiplied at the points where it is applied, so that the connecting pipes are reduced to a small size, the velocity of the air making up for a great force that formerly had to be communicated through rods, chains, or shafts. The principal object attained by the use of air to operate railway brakes is, however, to maintain a connection throughout a train by means of flexible pipes that accommodate themselves to the varying distance between the carriages. Presuming that the flow of air in pipes is not materially impeded by friction or angles, and that there will be no difficulty in maintaining lubrication for pistons or other inaccessible parts of machinery when driven by air, there seems to be many reasons in favour of its use as a means of distributing power in manufacturing districts. The diminished cost of motive power when  it is generated on a large scale, and the expense and danger of maintaining an independent steam power for each separate establishment where power is employed, especially in cities, are strong reasons in favour of generating and distributing power by compressed air, through pipes, as gas and water are now supplied.
"If you please."
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Finishing and fitting relates to giving true and accurate dimensions to the parts of machinery that come in contact with each other and are joined together or move upon each other, and consists in cutting away the surplus material which has to be left in founding and forging because of the heated and expanded condition in which the material is treated in these last processes. In finishing, material is operated upon at its normal temperature, in which condition it can be handled, gauged, or measured, and will retain its shape after it is fitted. Finishing comprehends all operations of cutting and abrading, such as turning, boring, planing and grinding, also the handling of material; it is considered the leading department in shop manipulation, because it is the one where the work constructed is organised and brought together. The fitting shop is also that department to which drawings especially apply, and other preparatory operations are usually made subservient to the fitting processes.ALONG THE MEUSE TO HUY, ANDENNE, AND NAMUR
"The orders issued by Monsieur Collins remain valid.The first impressions an apprentice forms of the smith-shop as a department of an engineering establishment is that it is a black, sooty, dirty place, where a kind of rough unskilled labour is performeda department which does not demand much attention. How far this estimate is wrong will appear in after years, when experience has demonstrated the intricacies and difficulties of forging, and when he finds the skill in this department is more difficult to obtain, and costs more relatively than in any other. Forging as a branch of work requires, in fact, the highest skill, and is one where the operation continually depends upon the judgment of the workman, which neither power nor machines can to any extent supplant. Dirt, hard labour, and heat deter men from learning to forge, and create a preference for the finishing shop, which in most places makes a disproportion between the  number of smiths and finishers.
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